Electronic power module

ABSTRACT

The inventive electronic power module is provided for effecting the smooth starting of motors. The module essentially includes two semiconductor elements, which are connected in an electrically anti-parallel manner and which are clamped between two metal bars, having a high thermal capacity, e.g. made of copper, by a pressing device. After being intermediately stored in the metal bars, the heat loss of the semiconductor elements is dissipated by cooling bodies placed on the metal bars.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/DE01/01566 which has an Internationalfiling date of Apr. 25, 2001, which designated the United States ofAmerica and which claims priority on German Patent Application number DE100 22 341.9 filed May 8, 2000, the entire contents of which are herebyincorporated herein by reference.

FIELD OF THE INVENTION

The invention generally relates to an electronic power module. Inparticular, it relates to one for an electronic motor control device forthe smooth starting of motors, with two semiconductor elements which areconnected in an electrically anti-parallel manner and with at least oneheat sink for dissipating the heat loss of the semiconductor elements.

BACKGROUND OF THE INVENTION

An electronic power module of the generic type is known as a componentpart of a power-electronic unit for the smooth starting of motors. Thepower-electronic unit here includes one or more electronic powermodules, which have to be designed for short-term loading. Theelectronic power module serves for carrying and influencing current in aphase, i.e., depending on whether there is a single-phase or three-phasesystem, an appropriate number of electronic power modules are required.

A power-electronic unit of this type only carries current in thestarting phase of the motor, the current being taken over in theoperating phase by a switching device connected in parallel.

In the smooth starting of motors, the current is only a fraction of thedirect starting current of the motor. Typically, the current duringstarting is 25% to 75% of the direct starting current. However, smoothstarting at reduced current results in a prolonged starting time for themotor in comparison with direct starting.

In the starting phase, very high power losses occur in thesemiconductors of the electronic power modules. By suitable combinationof the power module or power semiconductor and heat sink, it must beensured that the barrier-layer temperature permissible for thesemiconductors is not exceeded, to avoid their destruction. On accountof restricted space in the switch cabinet, there is also the requirementto minimize the amount of space needed for the electronic power modules.

An embodiment of an electronic power module in which two individualthyristors are connected in an anti-parallel manner and are pressedbetween two symmetrical halves of a heat sink is known but notdocumented by printed publications. One of the two halves of the heatsink is centrally divided and the two halves are connected by aflexible, electrically conductive connection. This makes it possible forthe thyristor disk cells to be pressed over their surface area, even ifthe height of the disk cells differs. The two halves of the heat sink ofthis known power section, which is designed both for short-term loadingand for continuous operation, are part of the power circuit and areconsequently under potential.

The short-term loading occurring in smooth starting causes a very highpower loss in the silicon cell, which leads to heating of the disk cellimmediately after loading begins. After approximately 2 to 5 seconds, aconstant temperature difference is established between the silicon celland the heat sink, i.e. the disk cell is thermally in the steady state,in which virtually the entire power loss is then used for heating theheat sink. The cooling of the power section is performed here by a fan.

SUMMARY OF THE INVENTION

An embodiment of the invention can be based on an object of providing anelectronic power module with good heat dissipation, high storagecapacity for the heat dissipated by the semiconductor elements in smoothstarting at the same time as a simple construction and low spacerequirement. An object may be achieved by at least two conducting bars,between which the two semiconductor elements are clamped by use ofpressure contacting. This configuration has the particular advantagethat the conducting bars no longer serve just for carrying current butcan, if made from a material with a high thermal capacity, serve as anintermediate store, from which the heat is passed on to heat sinksconnected to it and is dissipated.

It is particularly advantageous if the semiconductor elements areconfigured as semiconductor cells, for example as silicon cells.

If the two bars consist of a material with a thermal capacity greaterthan 1.8 Ws/K/cm³, such as aluminum for example, correspondingly goodheat dissipation can be achieved with them.

With regard to carrying current and heat, it is particularlyadvantageous however if the two bars include copper.

In an advantageous way, one of the two copper bars include hard copper.This copper bar can then be used as a component part of a pressingdevice for the pressure contacting mentioned above.

Furthermore, it proves to be particularly advantageous if a heat sink isconnected to the hard copper bar, since in this way an interface with alow heat transfer resistance can be achieved.

The second of the two copper bars advantageously includes electrolyticcopper, which is comparatively soft and deformable. If the second copperbar is made narrower in its central region, it is possible without anyproblem to compensate for small differences in thickness of thesemiconductor elements.

If the electronic power module is assembled with two further electronicpower modules of the same construction to form a three-phase unit, whichis operated in conjunction with a contactor, this allows a motor to beoperated in the starting phase and in continuous operation.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is explained in more detailbelow in an exemplary manner in conjunction with the drawings, in which:

FIG. 1 shows a side view of an electronic power module according to anembodiment of the invention for short-term loading,

FIG. 2 shows a further side view of an electronic power module accordingto an embodiment of the invention with a connected heat sink and

FIGS. 3, 4, 5 show side views of electronic power modules with differentcontacting.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The electronic power module according to an embodiment of the inventionas shown in FIG. 1 has two copper bars 1, 2 arranged in parallel,between which two silicon cells 3 have been introduced as semiconductorelements. The silicon cells 3 are configured as thyristors and arrangedsuch that they are turned through 180°, producing an electricallyanti-parallel circuit arrangement. Instead of thyristors, any otherdesired semiconductor components with a comparable function may beintroduced.

The copper bars 1, 2 perform the task of carrying the heat lossesoccurring during the high short-term loading away from the silicon cells3 as quickly as possible and storing them.

On account of the high volume-specific thermal capacity of approximately3.4 Ws/K/cm³ and the high thermal conductivity, copper is particularlywell suited as the material. The very good thermal conductivity ofcopper ensures very rapid removal of the lost heat from the silicon cell3 and at the same time leads to uniform distribution and heating of theremaining copper that is not in the direct vicinity of the silicon cell3. As compared with aluminum as a material for the bars, the dimensionscan be reduced by ⅓ third when copper is used, because of itsapproximately 1.5 times higher volume-specific thermal capacity.

In principle, materials other than copper are also suitable, providedthat they have a high thermal conductivity and a high volume-specificheat capacity. Alternatively, it would also be possible for example touse a combination of copper and a material which stores latent heat, forexample a phase changing material (PCM).

Each silicon cell 3 is pressed over its surface area between the copperbars 1 and 2 by use of a special pressing device 4. The pressing of thesilicon cells 3 leads to a pressure contact over the full surface areabetween the silicon cell 3 and the copper bars 1 and 2 and has theconsequence of a low electrical and thermal transfer resistance at thebearing surfaces.

The pressure contacting ensures a high resistance to alternating thermalloading and consequently a long service life of the power module, whichis necessary because of the exclusive operation with short-term loading.

The lower copper bar 1 in FIG. 1 includes harder copper, the uppercopper bar 2 consists of soft electrolytic copper. Threads 5 formounting the pressing devices 4 have been made in the lower copper bar1. By choosing the harder copper, bending of the lower copper bar 1 as aconsequence of the forces acting due to the pressing device is preventedto the greatest extent and the surface-area bearing of the silicon cells3 is ensured. Furthermore, tearing out or running away of the threads 5is prevented.

Fastened to the lower copper bar 1, for example by a screwed connection,is a heat sink 6 (see FIG. 2), in order to dissipate the heat lossesoccurring during the short-term loading. The use of harder copperprovides a largely surface-area contact between the copper bar 1 and theheat sink 6, and consequently a low thermal transfer resistance.

The upper copper bar 2 is made narrower in the center, to make itpossible to compensate for small differences in thickness of the siliconcells 3. This effect is also assisted by the use of soft electrolyticcopper for the upper copper bar 2. This measure ensures pressure contactover the full surface area between the silicon cells 3 and the uppercopper bar 2. It is possible here to dispense with a division of theupper copper bar 2 in the way provided by the prior art. By doing awaywith flexible, electrical connecting elements between the parts of thecopper bars, which are present in the case of the prior art, the overallheight of the electronic power module according to the invention can bereduced in comparison and the assembly effort can be reduced.

According to FIG. 2, the heat sink 6 is advantageously connected in anelectrically conducting manner to the lower copper bar 1. As a result,thermal transfer resistances are minimized and very good thermalcoupling of the heat sink 6 to the power module is achieved.Consequently, the heat sink 6 likewise contributes with its thermalcapacity to increasing the short-term loading capacity.

An electrically insulated attachment of the heat sink 6 with, forexample, an electrically insulating film is likewise possible. Onaccount of the approximately 3 to 5 times higher thermal transferresistance of such films, compared with direct attachment, thecontribution of the heat sink 6 to increasing the short-term loadingcapacity is reduced.

The upper copper bar 2 is made slightly narrower than the lower copperbar 1. This allows a plastic housing 7 to be attached around the uppercopper bar 2 and the pressing device 4 without increasing the overallwidth of the power module. A polymer composition is subsequentlyintroduced into the plastic housing 7 in order to ensure the dielectricstrength between the two copper bars 1, 2. The copper bars 1, 3, thesemiconductor cells 3 and the pressing device 4 are encapsulatedtogether to form a module.

The electrical contacting may take place at the end face on the lowercopper bar 1. The electrical connection to the upper copper bar may beconfigured differently, depending on the installation situationaccording to FIGS. 3, 4, 5. In FIG. 3, the contacting of the uppercopper bar 2 is performed within the housing 7 by means of a flat coppermaterial 8 bent in a U-shaped manner. In FIG. 4, a piece of copper bar 9taken perpendicularly upward and formed in a stepped manner at the lowerend is used for this purpose. FIG. 5 shows a connection of the twocopper bars 1 and 2 at their end faces.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. An electronic power module for the smooth starting of motors,comprising: two semiconductor elements, connected in an electricallyanti-parallel manner; at least one heat sink for dissipating heat lossof the semiconductor elements; and at least two conducting bars, betweenwhich the two semiconductor elements are clamped by pressure contacting;wherein one of the at least two bars includes hard copper; whereinanother one of the at least two bars includes electrolytic copper. 2.The electronic power module as claimed in claim 1, wherein thesemiconductor elements are configured as semiconductor cells.
 3. Theelectronic power module as claimed in claim 2, wherein the at least twobars include a material with a thermal capacity greater than 1.8Ws/K/cm³.
 4. The electronic power module as claimed in claim 1, whereinthe at least two bars include copper.
 5. The electronic power module asclaimed in claim 1, wherein a heat sink is connected to the hard copperbar.
 6. The electronic power module as claimed in claim 5, wherein thehard copper bar is connected in an electrically conducting manner to theheat sink.
 7. The electronic power module as claimed in claim 5, whereinan insulating film lies between the hard copper bar and the heat sink.8. The electronic power module as claimed in claim 1, wherein theelectrolytic copper bar is made relatively narrower in its centralregion.
 9. The electronic power module as claimed in claim 1, furthercomprising a pressing device for applying a mechanical pressure, bywhich the semiconductor elements are clamped.
 10. The electronic powermodule as claimed in claim 9, wherein the bars, semiconductor elementsand the pressing device are encapsulated with one another to form aunit.
 11. The electronic power module as claimed in claim 1, wherein theelectronic power module is an electronic motor control device for thesmooth starting of motors.
 12. The electronic power module as claimed inclaim 1, wherein the semiconductor cells are configured as thyristors.13. A multi-phase unit, comprising at least two of the electronic powermodules as claimed in claim
 1. 14. An electronic power module,comprising: a plurality of semiconductor elements, connected in anelectrically anti-parallel manner; at least one heat sink, adapted todissipate heat loss of the semiconductor elements; and at least twoconducting bars, between which the plurality of semiconductor elementsare clamped by pressure contacting; wherein one of the at least two barsincludes hard copper; wherein another one of the at least two barsincludes electrolytic copper.
 15. The electronic power module as claimedin claim 14, wherein the semiconductor elements are semiconductor cells.16. The electronic power module as claimed in claim 14, wherein a heatsink is connected to the hard copper bar.
 17. The electronic powermodule as claimed in claim 16, wherein the hard copper bar is connectedin an electrically conducting manner to the heat sink.
 18. Theelectronic power module as claimed in claim 17, wherein an insulatingfilm lies between the hard copper bar and the heat sink.
 19. Theelectronic power module as claimed in claim 14, further comprising apressing device for applying a mechanical pressure, by which thesemiconductor elements are clamped.
 20. The electronic power module asclaimed in claim 19, wherein the bars, semiconductor elements and thepressing device are encapsulated with one another to form a unit. 21.The electronic power module as claimed in claim 14, wherein theelectronic power module is an electronic motor control device for thesmooth starting of motors.
 22. The electronic power module as claimed inclaim 14, wherein the semiconductor cells are configured as thyristors.23. A multi-phase unit, comprising at least two of the electronic powermodules as claimed in claim 14.